The industry of semiconductor manufacturing involves highly complex techniques for integrating circuits within semiconductor materials. Due to the large scale of circuit integration and the decreasing size of semiconductor devices, the semiconductor manufacturing process is prone to processing defects. Inspection procedures are therefore critical to maintain quality control. Since the inspection techniques play an integral and significant part of the manufacturing process, the semiconductor industry constantly seeks more accurate and efficient testing procedures.
One type of inspection technique determines three-dimensional parameters of features within an integrated circuit device. For instance, such techniques can measure the height and sidewall angles of a trench pathway or the depth and sidewall slope of a contact via. One such technique referred to as stereoscopic reconstruction uses a scanning electron microscope (SEM) that obtains two separate images or line scans of a semiconductor feature. Each of the two images or line scans is obtained while the SEM is directed at the semiconductor feature in a unique incident angle. Each image or line scan is a different data set since the electron beam hits the feature at a different angle. The three-dimensional characteristics of the feature are determined by using elementary geometry. FIG. 1 illustrates a side plan, cross-sectional view a trench feature 100 inspected by stereoscopic reconstruction. θ1 and θ2 indicate the two incident angles at which each of the two images are taken; H represents the height of trench 100; and φ1 and φ2 represent each of the sidewall angles. Since only two sets of data are available, a simple trapezoid is constructed to approximate the feature under investigation. Unfortunately, such a simple technique typically produces estimations having poor precision and accuracy. Estimations generated by this technique can be useful when deviation from a process rather than absolute numbers is required, such as in a production environment. However, many processes require more accurate and detailed feature parameter information thereby revealing limitations of stereoscopic inspection.
Metrology atomic force microscope (AFM) is another inspection technique for determining feature parameter information. However, this is not reliable because the tip convolution is difficult to use and is much slower than SEM techniques. A destructive technique of focused ion beam (FIB) cross-sections is available, however, destructive techniques are less appealing due to its inherent requirement of rendering specimens useless.
In view of the foregoing, an inspection technique capable of accurately estimating detailed semiconductor feature information would be desirable.